Far from using the most sophisticated communications technology on the planet, many people seem to believe that they're connected to the other person by a pair of soup cans with a string stretched between them. Thus, they feel compelled to SCREAM at the top of their lungs whenever speaking on their cell phones.
Part of the problem is the extremely poor ear-piece design in most modern cell phones and the resulting inability for the person talking to get the right level of feedback. This is something that phone engineers had down to a finely tuned science a hundred years ago but seems to have been lost on current phone design engineers.
Fred: "Sorry, Bob. I didn't even realize that I was doing that."
Bob: "Well, it's not entirely your fault, part of it is that crappy phone. But still, get a grip. Your throat must be sore!"